Developer for dichroic iodine images



Feb. 27, 1951 E. H. LAND ET AL DEVELOPER FOR DICHROIC IODINE IMAGES Original Filed March 13, 1942 M zylzuToR i 4L 4,-

AT ORNEY Patented Feb. 27, 951

UNITED STATES lA'llEZI-V'l OFFICE DEVELOPER-FOR. nionnoro iomNeIMAGEs Edwin H, a, Cambridge, Jeseph Mahler,-

Brookline, and Mark Hyman, JrQCamb'ridgeQ' Mass, ass'ignors to ?olardid Corporation, Dani bridge, Mass, a corporation of ll)elaware oniginai application ,Ma'rch .13, 1942; Serial. No.

434L568! Divid d; hin i p ca ion Nove a.-

ber llg,1945 Seria1No. 6%,314

6 Claims. (o 95-83 of photographic developers for treating an image comprising an oxidizing-agent carried by photographic film, thedeveloper being of a character which effectsth'e replacement or conversion of theoxidizing imageto a dichroic stain as well as a developerwhichj'reacts with an oxidizing agent. ofsuitable oxidizing potential to cause the l as o o ne rom. he, dev o e Another object of the invention is to provide apllotographic developer for forming dichroic or i ht-pola iz n ima es n atr nsn' r molecua ly o en e inea o m r c as c. o X- a'mple, oriented" polyvinyl alcohol, which has "been rendered light. sensitive and exposed to light, particularly inolecularly oriented plastics hich h v eehjs hsi Zed h dichromates.

A further object o'fj e invention resides in the nr v s on i a e elope com i n acid S 'i n, i necrm reiqdide which mav' e d nase i ad pte' ftoha t en r i e h -ma er l of; which a H mageparryingiayer is formed, a reducing agent, a buffer for the acid and an agent ada ted q cont d j he g or o e ni d p o n t.

The invention accordingly comprises theplouuct possessing the features, properties and proportions of constituents, which are exemplified in the fdllOWing deta'il'e'dfdisclosure, andithe scope or" the. application of which will be indicated in the claims.

For a fuller understanding of the nature and objectsof the invention, reference should-be had to the following detailed description taken in connection with the accompanying drawing, in which;

Figure 1 is .a somewhat diagrammatic view illustrating a convenient arrangement for exposingthe sensitive material of the invention to light during the printing from a photographic negative;

Fig, 2 is a diagrammatic view in perspective illustrating ja print prepared in accordance with the. invention as .it appears when viewed without y i; nd

F s.-. 3 sa "s mi ar i w show ng the same pri t as it appears when viewed through a suitable 2 analyzer having,itSDOlQdizing axis at right angles tothe polarizing axis of said print.

The processof the present invention comprises three main steps.treatment of a sheet of the desired inaterial'with asuitable photo-sensitizing material, exposureofthesensitized sheet to light,

and. treatment. of the sheet with a developing agent adapted toproduce a. dichroic stain inthe exposed areasthereof, In addition to these steps, it may. be desirable in some cases to add a fourth step comprising treatment of the developed sheet an intensifieribath. Particular novell y lies in the fact thatlthe. stain which constitutes the image is produced by reaction between the developingaagentland the light-sensitive. material in the exposed areas ,of the sheet, the exposed inaterialcomprisingan oxidizing agent of sufiicient oxidizingpotential. to effect the release oi the ,dichroic stain.

Suitable sheet materials which mayv be nsed in thepractice of the invention include plastics,

particularly a plastic from. the class consisting of the linear, hydrophilic polymers, such for example as polyvinyl alcohol, polyvinyl acetal and regeneratedcellulose. Of the materials falling within this class, the preferred material is polyvinyl alcohol, .andprints. or images, formed in suitably prepared sheets of that material possess.thehighest.dichroisinland hence are most its len t Severalspecific examples and formulae will now be given, but it isto be understood that they are intended to be illustrative only. and are in no way to be construed-as limiting the invention to the specific times, proportions or percentages given. Itshould, moreover, be particularly noted that many variations may be made in anyof -the steps offthe invention, provided that said variations are compensated-form the. other steps,

as will be described in more detail hereinafter.

Byway of 'ill;ustration, the invention w iil be described with reference to a sheet of polyvinyl alcohol, and it will be assumed that the molecules therein have already been substantially oriented. The first step in the process is to render the sheet light-sensitive, and this may be done conveniently by imbibing the sheet in a solution containing the desired photo-sensitizing agent. Among the materials found suitable for this purpose, the preferred materials comprise dichromates, such for example as ammonium dichromate, potassium dichromate and sodium dichromate, with ammonium dichromate being particularly preferred for the reason that it is the most soluble.

The solvent for the photo-sensitizing agent may be simply water, but this is not wholly satis-- factory for the reason that it tends to penetrate the sheet too rapidly and thus tends to soften it unduly. It is preferable, therefore, to add to the solution a liquid which is miscible therewith but is a non-solvent of the plastic as well as nonreactive with the other chemicals present, and which accordingly tends to slow penetration of the sheet and thus aid in maintaining its stiffness. Suitable examples include acetone, methanol and ethylene glycol, and the volume thereof used may vary anywhere up to approximately 99% of the total volume of solvent present.

The proportion of sensitizing agent to solvent may vary within a wide range, from as low as 1 to 2% to as high as 40% based on the volume of solvent, provided the variation is compensated for by variation of the time of treatment approximately inversely to the proportion of sensitizing agent. Said time of treatment may vary from a few seconds upward but should preferably continue only long enough to permit the solution to penetrate the surface of the sheet uniformly for a short distance, and in no case should the sheet be allowed to soak so long that it softens unduly. It has also been found desirable to add a wetting agent such, for example, as soap or the product sold as Aerosol MA, a product of American Cyanamid and Chemical Corporation in order both to accelerate the sensitizing treatment and to promote uniform sensitization. Specific reference to the product Aerosol MA as dihexyl sodium sulfosuccinate may be found on page 11 of Handbook of Material Trade Names, Zimmerman and Lavine, Industrial Research Service, Dover, New Hampshire, 1946.

A typical satisfactory formula for the sensitizing bath is as follows:

Water cc 75 Acetone cc 25 Ammonium dichromate -gm 16 Aerosol MA gm 1 With a solution of approximately the foregoing formula, a sufficient time of treatment will be about two to three minutes, and the sheet should then be taken from the solution and the excess liquid wiped off or otherwise removed from its surface.

The next step of the process is to expose the sensitized sheet to the action of light. If the process is to be used to form a dichroic image of a photographic negative or the like, the exposure should be through the negative to be reproduced, as for example in the manner indicated in Fig. 1, wherein sensitized sheet is represented as mounted under a photographic negative l2 and exposed to light rays emanating from light source l4 provided with a conventional refiector l6. Light source I4 may emit primarily white light or primarily ultraviolet light, and the time of exposure may vary considerably, depending on the intensity of the light, the distance between it and the sheet, and the degree to which the sheet was sensitized, as pointed out above. If, for example, an R2 Photofiood bulb mounted approximately six inches from the surface of sheet IE! be used as the light source, a sheet sensitized as described above for two to three minutes should be sufficiently exposed in from forty to sixty seconds.

It should be noted that during the exposure, and particularly in the case of exposure for a long period, it may be advisable to shield sheet H] from the infrared rays emanating from the light source, as by means of a suitable filter I5. If it is desired to print by means of the ultraviolet rays emanating from source [4, element 15 should also include filtering material for visible light, and the exposure time should be increased to about five minutes, owing to the absorption of the ultraviolet light by negative 12.

The effect of the exposure of the sensitized sheet of the invention to light is to harden the surface of the sheet approximately proportionally to the degree of exposure. As will be seen from Fig. 1, the degree of exposure varies according to the variations of density in negative [2, i. e., more light is transmitted by the lighter areas of the negative than by the darker areas. The result is that the surface of sheet H] is hardened to a varying degree corresponding inversely to the density of negative l2. In other words, where the negative is lightest, sheet 10 is most exposed and most hardened, and where the negative is darkest, sheet ll] is relatively unexposed and remains relatively soft.

The next step in this embodiment of the process is to eliminate unexposed light-sensitive material from sheet ID. This may be done in the present example by a simple washing with water to remove the dichromate from the unhardened areas of the sheet, and the time of washing varies more or less according to the degree of sensitizing and the time of exposure, the important factors being that all unexposed dichromate should be removed but that the washing should not continue so long that the highlights of the picture are washed out or the exposed dichromate affected. It is for this reason that the sensitizing treatment is preferably confined to the surface of the sheet; the unexposed dichromate may then be removed in as short a time as possible. For a sheet sensitized and exposed as described above, the washing should be completed in approximately two minutes, but it must be emphasized that this time is by no means critical and may be varied considerably without appreciably altering the result.

The next step in the process is to treat the exposed and washed sheet with a developing compound adapted to react with the light-sensitive material in the exposed and hardened areas thereof to produce a dichroic stain. In the embodiment of the invention utilizing dichromate as the light-sensitive material, the developing compound comprises essentially an iodide solution of such characteristics and properties that it reacts with the dichromate in the sheet to produce the desired dichroic stain. In order to produce this reaction, the iodide or iodides used should be water-soluble and in addition should be easily oxidizable by the dichromate.

These characteristics in the developer may conveniently be secured either by using an alkali iodide, particularly ammonium iodide or an alkali metal iodide such, for example, as potassium iodide or sodium iodide, and adding one or more egmarv o 5 'acidsto thasolution, by'using a solution of "an iodid'e whicn is natura-ily easily oxidiza'ble such, for"example,-asierrous iodide orcerous iodide, 'or by using an iodide solution which is naturally acidic suchjfor example, as hydriodic acid. Preferred acids for use-in the first case include hy- '-dro'chlori'c' and 'h'ydrobromi'c. Alternatively, any strong oxidizing acid such, iorexainple, as sulphuric, nitric'or-phosphoric, or an organic acid such "asacetic may be used.

-It hasalreadybeen pointedout'that the re- --sult oithe exposure step illustrated inFigl-i's-to harden the surface of the sensitized sheet'differentia'lly, depending upon the. optical density of the photo'graphic negative at any given point. It followsrthereftire, that after the exposed sheet has been wa'she'd, the amount of diclironiate rerhaining'there'i'n'will similarly vary diiierentially overits"entire'area. Then when the sheet'is subjected to the developing treatment, theiodine stain absorbed in any particular area will depend upon the amount of dichroinate present-in that area. That is to say, the stain will be relatively intense in the areas Where there is considerable dichrornate, namely, the areas corresponding to light areas in the original negative. Conversely, there will be relatively little dichromate in the areas corresponding to the dark areas in the negative, and the amount of stain absorbed therein will therefore be substantially less.. In other words, the final product of the developing step of the'operation will be a positive reproduction in light-polarizing areas of the original negative imagerepresented by element i2 in Fig. 1.

As is the case with the other compounds and 3 steps of this invention, the composition of the developing'solution-1nay vary to aconsiderable extent, depending both on the results desired and on the Way in which the preceding steps were carried out. For example, if the sheet was sensitized in a concentrated solution and exposed for a relatively long period, a concentrated developer may be used, but if the sheet was sensitized in a dilute solution and exposed for a short time, the developer and developing time must be corre spondingly modified. Similarly, the particular acid used affectsthe developing time,'a developer containinga strong acid like hydrochloric requiring a shorter time than one containing a Weak acid like acetic. Several examples and formulae will'begiven, therefore, but it is to be understood that they are intended as illustrative only and the percentages and proportions therein are inno sense to be considered as critical.

A typical developer may be made up as follows:

Water i c'c io'o'o Acetone cc 80 Hydrochloric acid (38%) cc I 1.5 ammonium iodide gm 11.6 Potassium iodide a; grn 116 Boric acid gm 9.2

The acetone in the above formula is used for the same purpose as in the sensitizing bath,

preventing over-penetration by solvent. As explained above-any similarly acting agent may be substituted therefor, and the percentage thereof is optional and merely approximate. It has better results than either alone, but either may be used alone, and it will be noted that the total amount thereof should preferably be about 1%. Said percentage, however, is by no means critical.

n the contrary, it is possible to vary the iodide :7 \.'"DK- 6,0'.'

i3 eontent frofii :as l'ow a s 251% up to tiie saturation point, about40 -The hydrochlori'c acid contentin the'developing's'oliition should be kept relatively low, for otherwise I it tends to 'attack' and destroy the di- "chromatein the sheet. If, howeverjan oxidizing acid such as"sulphuric or nitric issubstituted for i the hydrochloric, the ameunt thereof may be sub- -stantially higher. The boric a'cid appearsto aid in" controlling the color-"of the finished-print.

A shet [sensitized an'd exposed as described above-will be sufiiciently developed afterfabout one r'ninute in a developer of aipproximatelythe -above rormma, and'the resultin'gp'rint willhave relatively even characteristicsand shading. If a more cohtias'ty =-pi"-int is desired, it inay be 0btained by adding to the' 'develober a suita'lbl'e r ecluci'ng agent, which'vvill suppress-anyfree iodine in the solution and-removed destroy any stain accidentally lproduce'd thereby in the unexposed areas' of the sheetjthusdighteningthe light areas in theiprint-andso'increasing itscontrast. It is also i desirable to add t'o'the developera weak alkali, which winemasabufier for theacidand thus aid'inlieeping uniform the action of the developer by maintaining the .pH value'th'ereof relatively constant.

Either a reducing ag'ent or an alkalior both together'may'be usedforthe above purposes, and a suitable compourid-for -'use in this connection "is the photographic develober sold as DK 60, a product of "Eastman Kodak Company, which 'will' act both as arr alkaliaiidas ared'ucin'g agent. Theahiount of this com pou'nd which sho'uld'be added to the i developer depends largely on the 1 degree of c'ontrast' desired in the prints, but in general it inay =b'e stated that satisfactory results are-obtained by using appfoX-ifnatelythe following illustrative formula:

BK-60 is a=silver halide developer-well 'kn'own to the' art'and specific reference thereto will be found in the handb'ook'entitled Photographic Chemicals and Solutions, 'Crabtree and Matthews, American Photographic Publishing Company' B-oston, "Massachusetts, 1938, on page 290, and 'under trie -heading (BK-=60) "As'ih the preceding case, a-sheetsensitiz'ed and "exposed as desoribedabovwshouldbe sufficiently developed-in the 'above de'veloper in aboutorie -niinute. -'If de'siredjhowever, thedegreeofcontrast' may bejiricreased by then treating" the sheet ih-an intensifying solution containinga reducing 'agent and preferably 'also'a' Weak alkali. This treatment will further-bleach and clear up the light areas, but care must'be'taken not to'connamely, to maintain the stiffness of the sheet by '65 -tin'ue it so long that-the highlights or other-areas -a're "affected. Ordinarily a minute should be suilicient, and a suitable illustrativeformula for such a bath is as' follows:

When the foregoing steps are completed, the print need only be wiped or otherwise dried and will then be finished. It will have approximately the appearance illustrated in Fig. 2, wherein print 20 bears a positive reproduction in dichroic areas of the image of negative l2, but the image will be relatively faint when viewed as in Fig. 2 without an analyzer. This is due to the fact that print 20, speaking in terms of optics, is merely an imperfect polarizer, which absorbs some of the light vibrating in one direction proportionally to the variations in density of its stained areas, but transmits the remainder of that component and all of the component vibrating in the opposite direction. In order, therefore, to see the image thereon properly, it should be viewed through a suitable crossed analyzer.

Such an arrangement is shown in Fig. 3, wherein a polarizing element 30 of uniform polarizing characteristics is shown superimposed on print 20, with its polarizing axis at right angles to that of the print, as indicated by arrows 25 and 35. The result is that analyzer 30 absorbs all of that component of the light which is freely transmitted by print 20. On the other hand, the analyzer transmits the other component of the light, which is the component differentially absorbed by the print, and will thus cause the image on print 20 to appear in as complete detail and with as high a degree of clarity as a photographic print of negative I2 produced by conventional photographic methods. Conversely, if analyzer 30 were rotated through 90 degrees with respect to print 20, it would then act to absorb the remainder of the component differentially absorbed by the print, with the result that the image would disappear and the combined elements would appear substantially uniformly transparent.

The process of the invention is well adapted to the production of dichroic stereoscopic images. For example, the image shown in Figs. 2 and 3 may be assumed to be one image of a stereoscopic pair. In that event the other image should be reproduced on a plastic sheet having its molecules oriented substantially at right angles to the direction of molecular orientation in sheet 20. The two sheets may then be superimposed with the images thereon in relative stereoscopic registry, and the resulting composite image will have a three-dimensional effect when viewed through proper polarizing viewing means in accordance, for example, with Patent No. 2,203,687.

The terms dichroism and dichroic as used herein and in the claims are intended to refer to the property of polarizing transmitted light by differential absorption according to vibration direction. It will be noted that in its simplest form the process of the invention may be practiced to produce a uniform dichroic light-polarizing sheet. This may be done, for example, by sensitizing a sheet of the desired molecularly oriented plastic, exposing the sheet uniformly to light, and then treating as described above to produce a uniform dichroic stain therein. It is to be understood that this and similar modifications of the process of the invention are to be construed as coming within the scope thereof.

It should be pointed out that it is not at all essential to the practice of this invention that the various steps of the process thereof be carried out continuously. For example, the sensitizing treatment may take place at an entirely different time from the remainder of the process. It should also be noted that these sheets are relatively low in light sensitivity, and that only moderate care need be taken to protect them from exposure to extraneous light while carrying out the other steps of the process of the invention.

It should be understood that many types of images other than photographic negatives may be reproduced by this process, such for example as a negative or positive of any other partially light-transmitting type or an opaque object of which it is desired to make a silhouette. The invention is particularly adapted, for example, to the reproduction of stencils, drawings, halftones, printed matter and the like. Negative l2 in Fig. 1 should be considered, therefore, as representative of any such similar medium which will differentially transmit or block light directed toward the sensitized sheet, and the reproductions therefrom made by the process of this invention will be positive reproductions, that is to say, the light values therein will be reversed with respect to said negative.

Although, as has already been pointed out, the process of the present invention is particularly adapted for the production of light-polarizing images, it is not limited thereto and may be used to produce non-polarizing images. In this modification of the invention, it is necessary only that the step of molecular orientation of the plastic sheet be omitted. If the process is carried out with this modification, the product will be substantially non-polarizing, positive reproduction of the original image comparable in substantially every respect with a positive print produced by conventional photographic technique.

As has been previously stated, the foregoing description is merely illustrative of one or more operative forms of the process of the present invention. It must again be emphasized that each step therein is a variable, and that none of the ingredients, times or proportions given for any step is critical except in so far as it may be made so by the other variables. Thus, in the sensitizing step, the time of treatment, sensitizing agent used, and the concentration of the solution are mutually dependent, and all must be considered in determining the proper exposure time. The degree of sensitizing and the degree of exposure, as well as the type of print desired, are mutually important to the choice of developer, and all four are governing factors in determining the developing time and the question of whether or not an intensifying bath should also be used. It follows, therefore, that great variation is possible and that virtually any degree thereof in one or more steps can be compensated for in the other steps. It is accordingly obvious that no set rules can be given and that it would be difficult if not impossible even to set outside limits on the ranges of variation.

Since certain modifications in the product which embodies the invention may be made without departing from its scope, it is intended that all matter contained in the foregoing description, or shown in the accompanying drawing shall be interpreted as illustrative and. not in a limiting sense.

What is claimed is:

l. A composition for developing light-exposed dichromate which forms an image in an imagecarrying layer of a hydrophilic, molecularly oriented, linear high polymer whereby to transform the dichromate to a dichroic material comprising iodine, said developing composition comprising water, hydrochloric acid, at least one easily oxidizable, water-soluble iodide salt, and an agent comprising boric acid for controlling the color of the iodine image formed by development of said dichromate, and wherein said composition is proportioned so that the hydrochloric acid thereof is restricted to a quantity lIlSlLncient to destroy dichromate undergoing development while the boric acid is present in a quantity suficient to exert a visible effect upon the color of the iodine image formed by development of said dichromate and the iodide salt is present in a concentration of from 0.5% to the saturation point of said composition.

2. A composition for developing light-exposed dichromate which forms an image in an imagecarrying layer of a hydrophilic, molecularly oriented, linear high polymer whereby to transform the dichromate to a dichroic material cornprising iodine, said developing composition comprising water, hydrochloric acid, at least one easily oxidizable, water-soluble iodide salt comprising ammonium iodide, and an agent comprising boric acid for controlling the color of the iodine image formed by development of said dichromate, and wherein said composition is proportioned so that the hydrochloric acid thereof is restricted to a quantity insuilicient to destroy dichromate undergoing development while the boric acid is present in a quantity sufiicient to exert a visible efiect upon the color of the iodine image formed by development of said dichromate and the iodide salt is present in a concentration of from 0.5% to the saturation point of said composition.

3. A composition for developing light-exposed dichromate which forms an image in an imagecarrying layer of a hydrophilic, molecularly oriented, linear high polymer whereby to transform the dichromate to a dichroic material comprising iodine, said developing composition con sisting of water, hydrochloric acid, at least one easily oxidizable, water-soluble iodide salt, an agent reactable with free iodine, and an agent comprising boric acid for controlling the color of the iodine image formed by development of said dichromate. I

4. A composition for developing light-exposed dichromate which forms an image in an imagecarrying layer of a hydrophilic, molecularly oriented, linear high polymer whereby to transform the dichromate to a dichroic material comprising iodine, said developing composition consisting of water, hydrochloric acid, at least one easily oxidizable, water-soluble iodide salt, a relatively weak alkali buffering said composition, a reducing agent, and an agent comprising boric acid for controlling the color of the iodine image formed by development of said dichromate.

5. A composition for developing light-exposed dichromate which forms an image in an imagecarrying layer of a hydrophilic, molecularly oriented, linear high polymer whereby to transform the dichromate to a dichroic material comprising iodine, said developing composition consisting of water, hydrochloric acid, at least one easily oxidizable, water-soluble iodide salt comprising ammonium iodide, an agent comprising boric acid for controlling the color of the iodine image formed by development of said dichromate, and an agent comprising a water-miscible liquid which is a non-solvent for the polymer of the image-carrying layer for slowing the penetration of the composition into the image-carrying layer.

6. A composition for developing light-exposed dichromate which forms an image in an image carrying layer of a hydrophilic, molecularly oriented, linear high polymer whereby to transform the dichromate to a dichroic material comprising iodine, said developing composition consisting of water, an acid selected from the class consisting of hydrochloric, hydrobromic, sulphuric, nitric, phosphoric, and acetic acids, at least one easly oxidizable water-soluble iodide salt comprising ammonium iodide, an agent comprising boric acid for controlling the color of the iodine image formed by development of said dichromate, and an agent comprising a Watermiscible liquid which is a non-solvent for the polymer of the image-carrying layer for slowing the penetration of the composition into the image-carrying layer.

EDWIN H. LAND.

JOSEPH MAHLER.

MARK HYMAN, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,214.940 Miller Feb. 6, 1917 1,482,613 John Feb. 5, 192 2,059,884 Mannes et al Nov. 3, 1936 2,059,887 Mannes et a1. Nov. 3, 1936 2,141,354 Gundelfinger Dec. 27, 1938 2,296,843 Gaspar Sept.'29, 1942 2,396,726 Trimble Mar. 19, 1946 

1. A COMPOSITION FOR DEVELOPING LIGHT-EXPOSED DICHROMATE WHICH FORMS AN IMAGE IN AN IMAGECARRYING LAYER OF A HYDROPHILIC, MOLECULARLY ORIENTED, LINEAR HIGH POLYMER WHEREBY TO TRANSFORM THE DICHROMATE TO A DICHROIC MATERIAL COMPRISING IODINE, SAID DEVELOPING COMPOSITION COMPRISING WATER, HYDROCHLORIC ACID, AT LEAST ONE EASILY OXIDIZABLE, WATER-SOLUBLE IODIDE SALT, AND AN AGENT COMPRISING BORIC ACID FOR CONTROLLING THE COLOR OF THE IODINE IMAGE FORMED BY COMMENT OF SAID DICHROMATE, AND WHEREIN SAID COMPOSITION IS PROPORTIONED SO THAT THE HYDROCHLORIC ACID THEREOF IS RESTRICTED TO A QUANTITY INSUFFICIENT TO DESTROY DICHROMATE UNDERGOING DEVELOPMENT WHILE THE BORIC ACID IS PRESENT IN A QUANTITY SUFFICIENT TO EXERT A VISIBLE EFFECT UPON THE COLOR OF THE IODINE IMAGE FORMED BY DEVELOPMENT OF SAID DICHROMATE AND THE IODIDE SALT IS PRESENT IN A CONCENTRATION OF FROM 0.5% TO THE SATURATION POINT OF SAID COMPOSITION. 